An IC or LSI available in the prior art usually has a circuit having a capacitor connected in series with ground, the circuit being arranged between the core domain and the input/output (I/O) domain of the IC or LSI. The function of the circuit is to prevent external noise from entering the major circuits of the IC or LSI and to expel noise toward the outside of the IC or LSI.
A semicustom IC or LSI has a plurality of unit cells arranged in a regular lattice pattern or in a matrix pattern. FIG. 1 illustrates the plan view of the unit cell of a semicustom LSI. In the drawing, the numeral 1 shows a unit cell having a P channel transistor 2 and an N channel transistor 11 therein. The P channel transistor 2 has an N.sup.- doped semiconductor layer 3 whose potential is selected to be identical to the substrate potential. The numeral 4 shows an N.sup.+ active area located in the N.sup.- doped semiconductor layer 3. The numeral 5 shows a P semiconductor substrate, the numeral 6 shows an N well produced in the P semiconductor substrate, the numeral 7 shows gates, the numeral 8 shows a P.sup.- doped semiconductor layer, the numeral 9 shows a P.sup.+ active area located in the P.sup.- doped semiconductor layer 8, and the numeral 10 shows a VDD line.
Incidentally, the N channel transistor 11 has a P.sup.- doped semiconductor layer 12 whose potential is selected to be identical to the substrate potential. The numeral 13 shows a P.sup.+ active area located in the P.sup.- doped semiconductor layer 12, the numeral 14 shows an N.sup.- doped semiconductor layer, the numeral 15 shows an N .sup.+ active area, the numeral 16 shows gates, and the numeral 17 shows a VSS line.
In order to fulfill the foregoing object, the foregoing capacitor is required to have a relatively large capacitance. This resultantly requires a large horizontal area on an IC chip. Since improvement in integration is one of the most important requirements for an IC or LSI, the foregoing structure of an IC or LSI is a big drawback which should be removed by all means.